Orthodontic brackets of the type to which this invention pertains are cemented by their base plates to the teeth of the row to be corrected, and the arch wire is inserted through the slots of all of the brackets attached to the row of teeth and are secured in position there by a ligature tongue which extends across the arch wire lying in the slot. In such devices, the closing spring member is movable between an open position allowing insertion of the arch wire into the slot and a closed position in which the at least one ligating tongue covers the arch wire. U.S. Pat. No. 6,942,483 is an example of this class of products.
Prior to the introduction of orthodontic brackets using such closing spring members with their ligating tongues, rings of elastic material were wrapped around tie wings formed on the upper structures. The use of closing spring members in place of elastic rings has facilitated changing of the arch wire, which must be done several times during the course of an orthodontic treatment. This has made such changing steps less time-consuming.
The interacting structures (i.e., closing spring member and base member) of the type of orthodontic brackets of which the invention herein is an improvement are now further described. The second end of the closing spring member is formed by tongues. At least one of such tongues is a latching tongue that is releasably engageable with an undercut of the second tie wing of the base-member upper structure, and at least one other of the tongues is a ligating tongue, which extends transversely across the arch-wire-receiving and, as noted above, covers the arch wire. The tongues forming the second end of the closing spring member are separated from each other by notches. The closing spring members are made of spring steel sheet and are stamped out.
One self-ligating orthodontic bracket of the prior art is, as mentioned above, that disclosed in U.S. Pat. No. 6,942,483. This device has a closing spring consisting of a spring steel sheet member which is permanently attached to the upper bracket structure. The spring member includes a latching tongue which is stamped out between two parallel ligating tongues. The latching tongue is bent essentially at a right angle to the ligating tongues and is bent again at its free end so that it can engage underneath a retaining projection formed on the upper bracket structure when the spring member is in the securing position—i.e., the position in which the ligating tongues extend transversely across the slot and the arch wire therein.
Another self-ligating orthodontic bracket of the prior art is known from U.S. Pat. No. 5,685,711. In such device, the closing spring consists of a ligating arm extending across the slot and a locking arm extending over and essentially parallel to the ligating arm. The two arms are connected to each other by a connecting section, which is bent into a circle and which cooperates with pins formed on the upper bracket structure to form a hinge. The closing spring can pivot between an open position, which makes the slot freely accessible, and a closed position. During production of such orthodontic bracket, the upper structure of the bracket is assembled from two halves which are essentially mirror images of each other, and the closing spring is inserted when the two halves are being assembled. Given that the two halves of the upper bracket structure are then welded together, it is impossible to replace the closing spring if it becomes damaged.
Still another self-ligating orthodontic bracket of the prior art is seen in U.S. Pat. No. 5,562,444. Such prior art bracket has a movable but captured closing spring, the closing spring being formed without a fork and being held immovably and undeformably only by its intrinsic elastic force in the opened or closed positions. More specifically, the force which the closing spring exerts on the arch wire is determined only by the type of material selected for the closing spring, and therefore cannot be adjusted. Such prior art patent also discloses projections on the second bracket tie wing, under which, in the closed position, the terminal edge of the closing spring lies so that the spring cannot be opened unintentionally. These projections are not able to produce any pre-tension in the closing spring.
It would be desirable to have closing spring members which are not essentially permanently attached to the orthodontic bracket base member, because permanent attachment makes it impossible to replace the closing springs if they become damaged. It would also be desirable for the closing spring members of such self-ligating brackets to be well secured in their closed position to prevent them from opening unintentionally. And, it would also be highly desirable that a closing spring member which is replaceable (because not permanently attached to the bracket base member) would be configured such that, when inserted into the bracket base member but still in the open position, would not fall out of its engagement with the bracket base member.